1. Technical Field of the Invention
The present invention relates to a video signal converter and a conversion method of video signal, respectively suitable to be applied when a video signal according to National Television System Committee (NTSC) is illustratively converted to a video signal corresponding to an extended graphics array (XGA), as well as an image display unit using the converter and conversion method, and a television receiver.
More particularly, the present invention relates to a video signal converter and others wherein a video signal of high image quality can be acquired in case the number of lines in a vertical direction or the number of pixels in a horizontal direction of the input video signal is converted so that it exceeds double for example, by increasing the number of lines in a vertical direction or the number of pixels in a horizontal direction thereof by n times according to an image adaptive conversion processing and further, increasing it by m times according to another conversion processing.
2. Description of the Related Art
Heretofore, devices for converting a video signal SNT according to NTSC to a video signal SXG corresponding to XGA and displaying an image on, for example, a liquid crystal display based upon the video signal SXG corresponding to XGA are proposed. The video signal SNT according to NTSC means a video signal according to an interlaced scanning method, in which the number of lines in a vertical direction thereof is 525. In such the video signal SNT, as shown in FIG. 1A, the number of effective lines in the vertical direction of each field is 240 and when a sampling frequency is 13.5 MHz, the number of effective pixels in a horizontal direction is 720. In the meantime, a video signal SXG corresponding to XGA is a video signal, for example, according to a sequential scanning method. In such video signal SXG, as shown in FIG. 1B, the number of effective lines in a vertical direction is 768 and the number of effective pixels in a horizontal direction is 1024.
Heretofore, an interpolation circuit 200 as shown in FIG. 2 is used as a video signal converter for acquiring a video signal SXG corresponding to XGA based upon a video signal SNT according to NTSC. In the interpolation circuit 200, a video signal SXG corresponding to XGA is generated by applying interpolation processing such as the nearest interpolation, linear interpolation and cubic interpolation to a video signal SNT according to NTSC.
As described above, the number of effective lines in the vertical direction of each field of the video signal SNT according to NTSC is 240 while the number of effective lines in a vertical direction of a video signal SXG corresponding to XGA is 768. Therefore, line number conversion processing of 3.2 times in relation to a vertical direction, in which 240 lines are converted to 760 lines, is executed in the interpolation circuit 200. If conversion exceeding double as described above is performed, the sharpness of an image is lost and an the quality of an image is deteriorated even if interpolation processing including many taps is used. xe2x80x98∘xe2x80x99 in FIG. 3A shows a video signal SNT according to NTSC. xe2x80x98xe2x97xafxe2x80x99 in FIG. 3B shows a video signal SXG corresponding to XGA after line number conversion. However, these indicate that the number of pixels in a vertical direction is merely increased.
The deterioration of the quality of an image described above is also similarly caused in case processing for converting the number of pixels in a horizontal direction to the number exceeding double is executed. Similarly, if a video signal SXG corresponding to XGA is acquired based upon a video signal SPL according to Phase Alternation by Line color television (PAL) with the number of lines in a vertical direction of 625, which is a video signal according to an interlaced scanning method, the quality of an image is also deteriorated.
The object of the present invention is to provide a video signal converter for acquiring a video signal of high image quality even if the number of lines in a vertical direction or the number of pixels in a horizontal direction of a video signal is converted to, for example, the number exceeding double, and others.
In carrying out the invention in one preferred mode, we provide a video signal converter comprising an image adaptive first converter for increasing the number of lines in a vertical direction or the number of pixels in a horizontal direction of a first video signal by n times to acquire a second video signal, and a second converter for increasing the number of lines in the vertical direction or the number of pixels in the horizontal direction of the second video signal by m times to acquire a third video signal.
Also, as another preferred mode of the invention, we provide a video signal conversion method comprising a first conversion step of increasing the number of lines in a vertical direction or the number of pixels in a horizontal direction of a first video signal by n times to acquire a second video signal by applying an image adaptive conversion processing to the first video signal, and a second conversion step of increasing the number of lines in the vertical direction or the number of pixels in a horizontal direction of the second video signal by m times to acquire a third video signal by applying a conversion processing to the second video signal.
As further preferred mode of the invention, we provide an image display unit comprising a video signal converter for converting the number of lines or the number of pixels of an input video signal to acquire an output video signal, and an image display for displaying an image based upon said output video signal. This video signal converter comprises an image adaptive first converter for increasing the number of lines or the number of pixels of a first video signal as said input video signal by n times to acquire a second video signal, and a second converter for increasing the number of lines or the number of pixels of said second video signal by m times to acquire a third video signal as said output video signal.
As further preferred mode of the invention, we provide a television receiver comprising a receiving section for receiving a television broadcasting signal, a video signal converting section for acquiring a converted video signal by converting the number of lines or the number of pixels of a received video signal received by said receiving section and an image display for displaying an image based upon said converted video signal. The video signal converting section comprises an image adaptive first converter for increasing the number of lines or the number of pixels of a first video signal as said received video signal by n times to acquire a second video signal and a second converter for increasing the number of lines or the number of pixels of said second video signal by m times to acquire a third video signal as said converted video signal.
According to the present invention, the image adaptive first converter performs image adaptive conversion processing to the first video signal to acquire the second video signal wherein the number of lines in a vertical direction or the number of pixels in a horizontal direction of the first video signal is increased by n times, for example, double. In the image adaptive conversion processing, the number of lines in a vertical direction or the number of pixels in a horizontal direction is converted not by mere interpolation processing using neighboring pixel signals but by acquiring required pixel signals according to estimation operation using, for example, a linear estimation expression. The second converter performs conversion processing to the second video signal to acquire the third video signal wherein the number of lines in a vertical direction or the number of pixels in a horizontal direction of the second video signal is increased by m times. In the conversion processing, the number of lines in a vertical direction or the number of pixels in a horizontal direction of the second video signal is converted by mere interpolation processing using, for example, neighboring pixel signals.
As described above, the second video signal is acquired by applying image adaptive conversion processing to the first video signal so that the second video signal has high image quality. The third video signal is acquired by applying conversion processing to the second video signal. The third video signal in which the number of lines in a vertical direction or the number of pixels in a horizontal direction of the first video signal is increased by xe2x80x98nxc3x97mxe2x80x99 times, is obtained by applying mere interpolation processing to the second video signal. The third video signal has high image quality and is free of the deterioration of the quality of an image.
In the invention, the image adaptive conversion processing is performed to the first video signal to acquire the second video signal wherein the number of lines in a vertical direction or the number of pixels in a horizontal direction of the first video signal is increased by n times. The conversion processing by, for example, interpolation is performed to the second video signal to acquire the third video signal wherein the number of lines in a vertical direction or the number of pixels in a horizontal direction of the second video signal is increased by m times. Thereby, the third video signal is finally increased by xe2x80x98nxc3x97mxe2x80x99 times of the first video signal in the number of lines in a vertical direction or the number of pixels in a horizontal direction. Therefore, even if the final conversion magnification of the number of lines in a vertical direction or the number of pixels in a horizontal direction is changed, conversion can be easily realized only by changing conversion magnification m in interpolation processing. That is, even if the final conversion magnification of the number of lines in a vertical direction or the number of pixels in a horizontal direction is changed, the existing image adaptive converter, for example, a double-speed converter can be used.
A further understanding of the nature and advantages of the invention may be realized by reference to the following portions of the specification and drawings.